1. Field of the Invention
The present invention relates generally to fluid flow control devices for controlling the flow of fluid along fluid flow pathways. More particularly, the invention concerns a highly novel fluid flow control device that has no moving parts and uniquely controls fluid flow by taking advantage of the properties of the fluid moving along the fluid flow pathway.
2. Discussion of the Prior Art
Various types of fluid flow control devices have been suggested in the past. Typically, these prior art devices use flow regulators, valves, diaphragms and like constructions all employing moving parts to achieve flow rate stabilization. Such constructions tend to be complex, costly and often of questionable reliability, particularly when used in medical applications.
Exemplary of a prior art flow regulator that embodies a deflectable beam placed within the fluid flow path is that described in U.S. Pat. No. 5,163,920 issued to Olive. The Olive device comprises a beam structure that is placed in the fluid flow path between an inlet and an outlet in a miniaturized housing. A flow gap defined between the beam and the housing provides a pressure differential between the faces of the beam which causes deflection and thus varies the fluid flow through the gap.
U.S. Pat. No. 3,438,389 issued to Lupin describes a flow metering orifice with automatic compensation for change in viscosity. Compensation for changes in viscosity in the Lupin device is effected by a movable valve element that shifts to increase the effective flow area as the viscosity of the fluid increases and to decrease the effective flow when the viscosity decreases.
The thrust of the present invention is to provide a highly novel flow control device that is of simple construction and design and is significantly more reliable than prior art flow control devices of conventional design. More particularly, the device of the present invention uniquely achieves flow rate stabilization by taking advantage of the properties of the moving fluid alone. In this regard, it is known that under certain circumstances eddy currents are generated as fluid moves past obstacles in the fluid flow path and the shape and magnitude of such eddies depend on the viscosity of the fluid. Further, it has been observed that the eddies themselves can be responsible for impeding the flow of fluid. Thus, arranging the size and position of obstacles in the fluid flow path can serve to provide viscosity dependent resistance to the flow of fluid. Therefore, the present inventor has determined that it is possible to design the fluid path so that the fluid flowing along the fluid path will generate its own regulation.
With the forgoing in mind, it is apparent that the method of flow rate stabilization contemplated by the present invention is fundamentally different in character from the prior art flow rate regulators that embody moving parts. Advantageously, because the devices of the present invention have no moving parts their manufacture is substantially easier and less expensive than conventional prior art flow rate stabilization devices.
An example of one form of a flow rate stabilization system contemplated by present invention comprises a device having a simple set of vanes or collars protruding from the sides of otherwise straight channels to provide for the delivery of fluid at a rate independent of viscosity. The vanes or collars of the device either have dimensions (primarily the dimension perpendicular to the current flow) or elastic constants relatively large so that under normal operating conditions their position and dimensions are constant. Advantageously, these types of vanes are quite easy to incorporate into an injection molded fluidic chip in which the vanes are merely an especially molded feature protruding from the walls of the fluid flow channel.